53© 2017 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria

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New data on the crystal morphology of brazilianite (Galiléia, Minas Gerais, Brazil)

R. I. Kostov1*, S. Dencheva2

1 University of Mining and Geology “St. Ivan Rilski”, Prof. Boyan Kamenov Str., Sofia 1700 2 Sofia University “St. Kliment Ohridski”, 15 Tsar Osvoboditel Blvd., Sofia 1504

Received October, 2016; Revised December, 2016

Morphology of brazilianite NaAl3(PO4)2(OH)4 crystals from the Galiléia area, Minas Gerais, Brazil (collection Ilia Deleff; Museum of Unique Crystals “Ilia Deleff”, University of Mining and Geology “St. Ivan Rilski”, Sofia) is studied by goniometry in order to determine the crystal forms. On 29 samples are decribed 25 crystallographic forms, among them 14 new forms. The majority of crystals are single terminated, spearhead-shaped, elongated along the [001] zone, with dominant crystal forms for the majority of the studied crystals: a {100}, b {010}, w {–201}, i {210}, q {121}, γ {–221} and δ {–223}. In several cases are found the faces of the following forms x {–101}, z {101}, θ {301}, µ {230}, g {–111}, o {111}, ε {–321}, ι {253} and ρ {122}. Crystal forms found in single cases are: for sample N4 ν {012}; for sample N10 c {001}, ζ {332}, η {546}, κ {–132}; λ {–532}; for sample N26 ξ {130}, n {011}; for sample N27 π {223}. A new specific for the area prismatic crystal habit of brazilianite is described – spearhead shaped long-prismatic habit. Brazilianite has a 2a/(b+c) = 1.29 ratio, which is representative for the (I)a structural type, according the crystal habit types of the paragenetic and crystal and chemical systematic of minerals. For the studied crystals the dominant crystal habit can be denoted as (I)a

[001].

Keywords: brazilianite, crystal habit, morphology.

Bulgarian Chemical Communications, Volume 49, Special Issue A (pp. 53–58) 2017

E-mail: rikostov@yahoo.com

INTRODUCTION

Brazilianite NaAl3(PO4)2(OH)4 has been reported for the first time from the Córrego Frio pegmatites, in the district of Linópolis, Minas Gerais in Brazil [1-6], and later on from several other occurrences in the country [7]: Minas Gerais – Araçuaí pegmatite district – Jenipapo[8], Conselheiro Pena pegmatite district – Divino das Laranjeiras [9], Telírio peg-matite, near Linópolis [5, 8, 10] as well as Gentil, Mendes Pimentel pegmatites [11, 8] and Săo Ge­raldo do Baxio pegmatites [8]; Espírito Santo – Santa Teresa and Mantena [12]; Paraíba – Pedra Lavrada – Alto Patrimônio; Rio Grande do Norte – Equador (Alto do Giz pegmatite) and Parelhas (Boqueirão or Boqueirãozinho pegmatite). Beside Brazil, the mineral is reported from pegmatites in several countries worldwide [13]. Brazilianite be-longs to the class of phosphates and crystallizes in the P21/n space group of the Monoclinic System,

with a=11.233 (6) Å, b=10.142 (5) Å, c=7.097 (4) Å and β=97.37 (2)° [14].

ExPERIMENTAL

Brazilianite crystals and aggregates from the Galiléia pegmatites in the Rio Doce Valley, about 40 km southeast from Governador Valadares, south of Divino das Laranjeiras, Minas Gerais, are on dis-play at the Museum of Unique Crystals “Ilia Deleff” at the University of Mining and Geology “St. Ivan Rilski” in Sofia (labeled Galiléia, Minas Gerais; col-lection Ilia Deleff). The Galiléia mine area includes also the type locality for brazilianite Córrego Frio mine. The pegmatites belong to the pegmatite dis-trict Conselheiro Pena, which is part of the Eastern Brazilian Pegmatite Province in the state of Minas Gerais. Most of the pegmatites in that region are hosted in the quartz biotite-schist of the São Tomé formation linked to the Urucum granite – they are orientated in most cases in the NW-SE direction [8]. Brazilianite is described as a hydrothermal mineral in phosphate-rich zones of the granite pegmatites. The mineral association for the Córrego Frio type

54

pegmatite is: muscovite, albite, quartz, fluorapatite, souzalite, scorzalite, arsenopyrite, beraunite, chil-drenite, dufrenite, frondelite, garnet, jahnsite, ro-scherite, sabugalite, strunzite, tapiolite, tourmaline, uraninite, wyllieite and zircon [5].

Twenty nine brazilianite crystals from the Galiléia area, Conselheiro Pena district, state of Minas Gerais in Brazil were chosen for study. The majority of brazilianite crystals are not double ter-minated. Most of the brazilianite samples are frag-ments of crystals or such of a poor termination. They are transparent to semi-transparent (Fig. 2–3). In some of the large brazilianite aggregates the crys-tals are whitish and not transparent. The brazilianite crystals (University of Mining and Geology – main-ly from inv. N K222; Sofia University N M6229), were measured on a optical contact (Optische Universal-Winkelmesser, Carl Zeiss) and one-circle (E. Fluess, Steglitz, Berlin) goniometer to determine crystal morphology. The average dimensions for the largest 16 crystals are: 3.6×2.2×1.3 cm.

x-ray data were received on a TUR-M62 (Fa-culty of Geology and Geography, University of Sofia “St. Kliment Ohridski”) powder diffractom-eter in the region 2Θ 4–80°, CoKα radiation, 40 kV, 15 mA and on a Bruker-D2 Phaser (with a Diffrac.eva V4.0 search­match software) in the region 2Θ 5–70°, CuKα radiation, 30 kV, 10 mA (University of Mining and Geology “St. Ivan Rilski”).

RESULTS AND DISCUSSION

The x-ray pattern of brazilianite (Fig. 1) cor-responds to the standard one [15]. The x-ray pat-terns of the Palermo and Brazilian material also cor-

respond – for the Palermo mine, New Hampshire, USA d (Å): 5.04 (10), 2.98 (8), 2.73 (8), 2.68 (8), 2.87 (7), 1.44 (5), 3.77 (4) [16]. The x-ray powder pattern in several crystals yielded a peculiarity in the range of 4–64°: the °2Θ diffraction lines 311, 122, 231, 510, 142, 251, 611 and 433 are widened or even doubled in all investigated samples, with additional lines of smaller intensity on lower °2Θ (e.g. on ~31° 2Θ) [8].

Twenty five crystallographic forms were record-ed (Table 1). Dominant are the forms: a {100}, b {010}, w {–201}, i {210}, q {121}, γ {–221}, and δ {–223} (Fig. 2, 4). Drawings are made with the help

Fig. 1. x-ray powder diffraction of brazilianite

Fig. 2. Brazilianite crystal with double termination faces (sam-ple N5; 4×2×1.5 cm)

R. I. Kostov, S. Dencheva: New data on the crystal morphology of brazilianite (Galiléia, Minas Gerais, Brazil)

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Table 1. Distribution of more than one observed crystal forms on the studied brazilianite crystals

N a{100}

b{010}

w{–201}

x{–101}

z{101}

θ {301}

i{210}

µ{230}

q{121}

g{–111}

o{111}

γ{–221}

δ{–223}

ε{–321}

ι {253}

ρ{122}

1 + + + + +2 + + + + + +3 + + + + + + +4 + + + + + + +5 + + + + + + +6 + + + +7 + + + + + + + +8 + + + + + + + + +9 + + + + + + +

10 + +11 + + + + + + + +12 + + + + + + + + + +13 + + + + + + + + + +14 + + + + + + + +15 + + + + + + +16 + + + + + +17 + + + + + + + + +18 + + + + + + + + +19 + + + + + + + +20 + + + + + +21 + + + + + + +22 + + + + + +23 + + + + + + + +24 + + + + + +25 + + + + +26 + +? + + +27 + + + + +28 + + + + + + +29 + + + + + +

of a VESTA program [17]. Some faces in the [001] zone are striated along the crystallographic axis c or display striations in a curvilinear pattern. All stri-ated forms in the [001] zone exhibit multiple sig-nals. Crystals are typically prismatic, or spearhead-shaped, elongated along the [001] zone, with large faces of the forms w {–201}, i {210}, and γ {–221}, and subordinate or rare forms as a {100}, c {001}, b {010}, q {121}, as well as x {–101}, g {–111}, o {111}, ε {–321}, ζ {332}, η {546}, θ {301}, ι {253} and z {101}. The front (1st) pinacoid a {100} and 2nd pinacoid b {010} are represented by elongated narrow faces in the prism zone. The basal (3rd) pi-nacoid c {001}, as a tiny face, is rarely observed. Two brazilianite crystals (N28-29) display a simi-lar prismatic zone morphology with the majority of crystals, but with a different termination including forms θ {301}, ι {253} and z {101}. They can rep-resent a morphological subtype (Fig. 3, 5). Sample N10 also displays a different bipyramidal-type habit. In several cases are found the faces x {–101},

Fig. 3. Brazilianite crystal with single termination faces (rare crystal habit; sample N1; 4×3×2 cm)

R. I. Kostov, S. Dencheva: New data on the crystal morphology of brazilianite (Galiléia, Minas Gerais, Brazil)

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z {101}, θ {301}, µ {230}, g {–111}, o {111}, ε {–321} ι {253}, and ρ {122}. Crystal forms found in single cases are: for sample N4 ν {012}; for sample N10 c {001}, ζ {332}, η {546}, κ {–132} and λ {–532}; for sample N26 ξ {130} and n {011}; for sample N27 π {223}.

In the first publication on brazilianite 18 crystal forms have been distinguished, but some crystallo-graphic descriptions (as “bipyramid”; “dome”) turn to be incorrect, including the spherical coordinates for the m {110} form [1]. Several different habits of investigated brazilianite crystals have been dis-tinguished, primarily on the basis of the elongation and orientation of the crystal, but relative develop-ment of the forms was considered as well [8]: the first group of crystal habits is represented by the elongation along [101] (this group could be divided into four subgroups on the basis of different form development); the second habit is represented with crystals from the Jenipapo pegmatite, Araçuaí dis-trict, which are elongated along [001] and terminat-ed with a large {011} form, giving the crystal the form of a sharp column; the third group (new habit)

is represented with crystals from the Gentil pegma-tite (G5) and the São Geraldo do Baixio group (S1) – the crystal S1 is tabular, flattened along [001] with a large development of {101}, while crystal G5 exhibits a similar, although slightly less flattened habit; the fourth group (new habit) is represented by a crystal from the São Geraldo do Baixio group (S3) which appears somewhat isometric, due to the large development of {110} prism as well as {010}; the fifth group is represented with crystals from the Rapid Creek, Yukon, Canada, with an extremely elongated along [001] crystal habit.

In another morphological overview four types of crystal habits are distinguished: short-prismatic to the c-axis with the crystal forms {100}, {010} and {110} parallel to the c-axis (“Brazil habit”); short-prismatic to the a-axis with crystal forms {100}, {110}, {–101}, {–301}, {011}, {111}; “dipyrami-dal” on the a-axis with crystal forms {011}, {111} (“Palermo habit”); “dipyramidal” on the c-axis [13].

The arrow-like or spearhead shaped prismatic habit is also a new crystal habit among the described brazilianite habits from Brazil. Such prismatic habit can be placed between the S3 short prismatic bra-zilianite type habit from São Geraldo do Baixio group pagmatites in Brazil and the extremely long prismatic habit of crystals from Rapid Creek area, Yukon, Canada [8].

Fig. 4. Drawing of a typical crystal habit with common crys-tal forms for the majority of the studied brazilianite crystals in standard orientation (VESTA program)

Fig. 5. Drawing of the rare crystal habit for brazilianite (VESTA program)

R. I. Kostov, S. Dencheva: New data on the crystal morphology of brazilianite (Galiléia, Minas Gerais, Brazil)

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According to its structural anisometricity, brazil-ianite can be regarded as of a pseudo-isometric type structure – one can compare the forms of the simi-lar in symmetry monacite-(Ce) in the monoclinic system [18]. The structure of brazilianite with a 2a/(b+c) = 1.29 ratio is representative for the (I)a structural type. For the studied crystals the domi-nant crystal habit can be denoted as (I)a

[001] accord-ing the crystal habit types of the paragenetic and crystal and chemical systematic of minerals [18].

CONCLUSIONS

Goniometric studies of 29 crystals of brazili-anite from the Galiléia area (Minas Gerais, Brazil) revealed 25 crystallographic forms, among them 14 new forms. The majority of crystals are single terminated, spearhead-shaped, elongated along the [001] zone, with dominant crystal forms a {100}, b {010}, w {–201}, i {210}, q {121}, γ {–221} and δ {–223}. In several cases are found the forms x {–101}, z {101}, θ {301}, µ {230}, g {–111}, o {111}, ε {–321}, ι {253} and ρ {122}, and in single cases the forms ν {012}, c {001}, ζ {332}, η {546}, κ {–132}; λ {–532}, ξ {130}, n {011} and π {223}. A new specific for the area prismatic crystal habit of brazilianite is de-scribed – spearhead-shaped long-prismatic habit, denoted as (I)a

[001].

Acknowledgments: The authors would like to thank L. Mihaylov (University of Mining and Geology “St. Ivan Rilski”) and V. Nakova (University of Sofia “St. Kliment Ohridski”) for the X-ray data of brazilianite and associated minerals.

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1. F. H. Pough, E. P. Henderson, American Mineralogist, 30, 572 (1945).

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of Mineralogy, John Wiley, New York, 1951. 4. J.-P. Cassedanne, Revue de Gemmologie, 68, 9, 14

(1981).5. J.-P. Cassedanne, Mineralogical Record, 14, 227

(1983).6. R. B. Cook, Rocks & Minerals, 75, 40 (2000).7. C. Cornejo, A. Bartorelli, Minerals and Precious

Stones of Brazil, Solaris, Sao Paulo, 2010.8. A. Čobić, V. Zebec, R. Scholz, V. Bermanec, S. de

Brito Barreto, Natura Croatica, 20, 1 (2011).9. V. Bermanec, N. Tomašić, G. Kniewald, R. Scholz,

G. M. Da Costa, A. H. Horn, J. Karfunkel, 32nd International Geological Congress, Abstracts, Part 1, Firenze, IUGS, 215 (2004).

10. G. D. Gatta, P. Vignola, M. Meven, R. Rinaldi, Amer. Mineral., 98, 1624 (2013).

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12. G. Niedermayr, Ann. Naturhistor. Mus. Wien, 76, 605 (1972).

13. K.-L. Weiner, R. Hochleitner, Lapis, 22, 1, 8 (1997).14. B. M. Gatehouse, B. K. Miskin, Acta Cryst., 30,

1311 (1974).15. JCPDS International Center for Diffraction Data,

Power Diffraction File, Swarthmore, PA, 1991.16. C. Frondel, M. L. Lindberg, Amer. Mineral., 33, 135

(1948). 17. K. Momma, F. Izumi, J. Appl. Crystallogr., 44, 1272

(2011).18. I. Kostov, R. I. Kostov, Crystal Habits of Minerals

(Bulgarian Academic Monographs, 1), Co-published by Pensoft Publishers and Prof. Marin Drinov Academic Publishing House, Sofia, 1999.

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R. I. Kostov, S. Dencheva: New data on the crystal morphology of brazilianite (Galiléia, Minas Gerais, Brazil)

Нови даННи върху кристаломорфологията На бразилиаНит (галилея, миНас жераис, бразилия)

р. и. костов1, с. денчева2

1 Минно-геоложки университет „Св. Иван Рилски“, ул. „Проф. Боян Каменов“, 1700 София 2 Софийски университет „Св. Климент Охридски“, бул. „Цар Освободител“ № 15, 1504 София

Постъпила октомври, 2016 г.; приета декември, 2016 г.

(резюме)

изучена е кристаломорфологията на 29 кристали от бразилианит NaAl3(PO4)2(OH)4 от района галилея в щат минас жераис в бразилия (колекция на музея на уникалните кристали „илия делев“ при минно­геоложкия университет „св. иван рилски“, софия). установени са 25 кристални форми, от които 14 нови кристални форми. Повечето от бразилианитовите кристали са еднокрайни, копиевидно оформени, удълже-ни по [001] зоната, с доминиращи кристални форми i {210}, a {100}, w {–201}, γ {–221}, q {121}, δ {–223} и b {010}. описан е нов дългопризматичен хабитус за този минерал, който съгласно парагенетичната и криста-лохимичната класификация на минералите може да се отнесе към (I)a

[001] хабитусния тип.